In ultrasonic systems used to image the interior of a patient's body, a transducer transmits acoustic energy into the body and receives echoes from structures therein. It converts the energy in these echoes into electrical signals that are used to form an image. In many cases, structures close to the surface of the body are not in a region of sharp focus because of their proximity to the transducer, but they can be placed farther away from the transducer so as to be in a region of better focus by insertion of a stand-off device between the transducer and the patient's body. A plastic bag filled with liquid may be used for this purpose. Furthermore, in a system producing an image in the form of a sector, it is difficult to identify structures near the apex because of the limited field of view. This problem can also be eliminated by use of a stand-off device because the structures previously at the apex can be placed properly within the sector where more of the surrounding structure is visible.
In some known stand-off devices, the surface of the stand-off device that contacts the body has been made of flexible material, but the volume within the device has been filled with liquid so that pressure must be applied to bring a desired amount of the surface into intimate contact with the patient's body. This causes the relative positions of the structures being observed to be disturbed.